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  • 1
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of solar radiation on photosynthetic oxygen production, pulse amplitude-modulated (PAM) fluorescence and pigmentation were measured in the Mediterranean brown macroalgaPadina pavonica (Linnaeus) Lamouroux under field conditions and natural sunlight. Exposure of thalli to solar radiation for 1 h caused a dramatic decrease of their photosynthetic quantum yield, which recovered to initial levels after they had been placed in the shade for 3 h. Photoinhibition also occurred at the natural growth site ofP. pavonica during the hours of maximal solar irradiance. Photosynthetic oxygen production was also affected by high levels of solar radiation both in algae harvested from the surface and from 6 m depth; oxygen production started to decrease after a few minutes of exposure, and negative values were found after 1 h of solar exposure. Chlorophylla content inP. pavonica also decreased during the hours of maximal solar irradiation. These results suggest that photoinhibition ofP. pavonica occurs during part of a typical summer day on Mediterranean coasts.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of solar and artificial ultraviolet radiation on the motility and graviorientation of three strains of the dinoflagellate Prorocentrum were studied. P. micans isolated from the Baltic Sea shows a pronounced negative gravitaxis which switches to a positive one even after short exposure times to either solar or artificial UV irradiation. In constrast P. minimum strains isolated from the Kattegat and the Atlantic coast off Portugal showed only a weak upward orientation. In all three strains the linear swimming velocity decreases after short exposure times and, in addition, the percentage of motile cells in the populations drastically decreases. Removing the ultraviolet component of solar radiation with a cut-off filter prolongs the tolerated exposure times.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 147 (1987), S. 179-183 
    ISSN: 1432-072X
    Keywords: Dichroic orientation ; Euglena gracilis ; Flagellate ; Gravitaxis ; Photomovement ; Phototaxis ; Polarotaxis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A fully automatic computer-controlled video analysis system has been used to study the movement of the green unicellular flagellate, Euglena gracilis in a horizontal or vertical cuvette. In darkness, in the absence of gaseous gradients, most cells swim straight upwards. While in a horizontal cuvette the transition between positive and negative phototaxis is found at about 1.5 W m-2, an excess of 30 W m-2 is required to reverse the upward swimming (due to the combined stimulus of negative gravitaxis and positive phototaxis) in a vertical cuvette. By studying the swimming direction in horizontal and vertical cuvettes in polarized light irradiated from above or from the side, respectively, the dichroic orientation of the photoreceptor molecules can be determined in three dimensions with respect to the axes of the cell: In a horizontal cuvette, in a linearly polarized beam from above, the cells orient predominantly at an angle of about 30° clockwise off the electric dipole transition moment as seen from above. The behavior in a vertical cuvette with polarized light entering from above indicates that the photoreceptor pigments are dichroically oriented 60° counterclockwise from the flagellar plane (seen from the front end of the cell). Experiments with horizontal polarized light indicate that the photoreceptor transition moment deviates 25° clockwise off the long axis of the cell.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 20 (1991), S. 101-107 
    ISSN: 1432-1017
    Keywords: Euglena gracilis ; Gravitaxis ; Image analysis ; Microgravity ; NIZEMI (slow rotating centrifuge microscope) ; Velocity of movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Motility and orientation has been studied in the unicellular photosynthetic flagellate, Euglena gracilis, using real time image analysis capable of tracking up to 200 cells simultaneously in the slow rotating centrifuge microscope (NIZEMI) which allows one to observe the cells' swimming behavior during centrifugation accelerations between 1 g and 5 g. At 1 g the cells show a weak negative gravitaxis, which increases significantly at higher accelerations up to about 3 g. Though most cells were capable of swimming even against an acceleration of 4.5 g, the degree of gravitaxis decreased and some of the cells were passively moved downward by the acceleration force; this is true for most cells at 5 g. The velocity of cells swimming against 1 g is about 10% lower than that of cells swimming in other directions. The velocity decreases even more drastically in cells swimming against higher acceleration forces than those at 1 g. The degree of gravitactic orientation drastically decreases after short exposure to artificial UV radiation which indicates that gravitaxis may be due to an active physiological perception rather than a physical effect such as an asymmetry of the center of gravity within the cell.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Secondary carotenoids are suspected to modulate photomovement in Haematococcus lacustris [Girod] Rostafinski (Volvocales). To investigate the influence of these extrachloroplastic ketocarotenoids on phototactic and photophobic responses in the flagellate stage of the green alga, flagellate suspensions differing in the content of secondary carotenoids were grown from green and red aplanospores. Photo-orientation of these flagellates induced by unilateral irradiation was investigated using a computer-aided system for microscopic image analysis. Results were hypothetically summarized as follows:(1) Diminution of precision of the positive phototaxis was found in red flagellates. This might be due to cellular shading of the blue-light-sensitive photoreceptor by secondary carotenoids.(2) Red flagellates exhibited an increase in the photophobic response. This finding is discussed in relation to an adaptive increase of the photoreceptor sensitivity, thought to be a result of the higher optical density of the corresponding cell suspension in the blue wavelength region.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Inhibition of photosynthesis after exposure to solar radiation was investigated in the marine green alga Dunaliella salina by monitoring photosynthetic optimal quantum yield Fv/Fm and efficiency of oxygen production. Samples were exposed to solar radiation in Ancient Korinth, Greece (37°58′ N, 23°0′ E) in August 1994. Within 30 min, Fv/Fm and efficiency of oxygen production decreased with similar kinetics with increasing exposure time. The inhibition, however, diminished when ultraviolet radiation was progressively excluded by means of colour filter glasses. Samples exposed for 3 h showed complete or partial recovery of photosynthesis, with almost the same rate under all irradition conditions. The fit of the experimental data with an analytical model describing inhibition of photosynthesis as a function of a linear combination of the photon fluence in the UV-B, UV-A and PAR allows one to estimate the relative mean effectiveness for inhibition by the three spectral ranges [about 2 × 10−4, 4 × 10−6 and 2 × 10−7 (μmol photons m−2)−1 for UV-B, UV-A and PAR, respectively].
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Planta 203 (1997), S. S7 
    ISSN: 1432-2048
    Keywords: Key words: Euglena ; Flagellates ; Gravitaxis ; Graviperception (threshold) ; Gravireceptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In the flagellate Euglena gracilis Klebs,␣gravitaxis is mediated by an active physiological receptor and is not the result of passive alignment of the cells in the water column. The threshold of this response was found at 0.08 〈 threshold 〈0.16 g during a recent space flight on the American shuttle Columbia, where the cells were subjected to different accelerations between 0 and 1.5 g; the response saturated at 0.32 〈 saturation ≤ 0.64 g. Over the whole duration of the mission no adaptation of the response to microgravity was observed. The whole body of the cell, rather than intracellular organelles, seems to act as statolith since suspending the cells in a density-adjusted medium (Ficoll) resulted in an inhibition of gravitaxis and even reversal of orientation at higher densities. Thus, the cytoplasm seems to exert a pressure on the respective lower membrane where it is hypothesized to activate stretch-sensitive specific ion channels, as indicated by inhibitor studies with gadolinium. One of the early steps in the sensory transduction chain seems to be a modulation of the membrane potential since ion-channel blockers, ionophores and ATPase inhibitors strongly inhibit gravitaxis in this flagellate without seriously affecting motility and phototaxis.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-5052
    Keywords: Outdoor UV-B ; UV-A ; PAR measurements ; Spectral balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Daily and weekly fluctuations of PAR, UV-A, and UV-B have been continuously monitored for 5 months in Ancient Korinthos, Greece (37°58′ N, 23°0′ E) using a calibrated instrument based on 3 sharp band sensors. Daily dose ranged between 521–12 006 kJ m-2 for PAR; 52–1, 239 kJ m-2 for UV-A; and 0.66–22.5 kJ m2 for UV-B. Weekly dose ranged between 16 778-81 788 kJ m-2 for PAR; 1 406–8 517 kJ m-2 for UV-A; and 18–151 kJ m-2 for UV-B. UV-B/PAR and UV-A/PAR ratio distribution, however, does not follow closely PAR fluctuations. Generally, the UV-B/PAR and UV-A/PAR ratios were high in bright light conditions (2.1×10-3, 118×10-3) and low in darker weeks (0.9×10-3, 63×10-3. The UV-B/UV-A ratio exhibits smaller fluctuations with season (20x1×10-3, 12×10-3). Attention is drawn to the effects of sudden changes in ambient radiation and to the ratios of UV-B, UV-A, and PAR.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 128 (1997), S. 5-13 
    ISSN: 1573-5052
    Keywords: Aquatic ecosystems ; Light penetration ; Macroalgae ; Phytoplankton ; Solar UV-B radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of short wavelength solar radiation on aquatic ecosystems were studied in several marine and freshwater systems. The spectral distribution and the penetration of solar radiation into different water types (coastal and oceanic waters of the Baltic Sea, North Sea, Atlantic and Mediterranean) were investigated. Penetration of short wavelength solar radiation strongly depends on the content of dissolved and particulate substances as well as the concentration of phytoplankton. The primary producers often show a typical vertical distribution within the euphotic zone and are reached as well as affected by the penetrating UV-B radiation. The effect of this radiation was both determined in phytoplankton and macroalgae. Measuring pulse amplitude modulated (PAM) fluorescence indicated that major biomass producers were severely inhibited by surface radiation and even impaired at their natural growth site. Likewise, photosynthetic oxygen production was affected by extended exposure to solar radiation.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 133 (1997), S. 236-238 
    ISSN: 1573-5052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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